Climate Change Killed Off The Mayas (Are We Next?)

Caracol, a Mayan archaeological site in Belize. Carocal
was a crucial population center during the Classic Maya
period.Douglass Kennett, Penn
State

Much has been made of the so-called 2012 Mayan apocalypse. But
for the real Maya people, the end of the world came slowly and
timed with historic droughts.

A new, ultra-detailed climate record from a cave in Belize
reveals
Classic Maya civilization collapsed over centuries as rain
dried up, disrupting agriculture and causing instability that led
to wars and the crumbling of large cities. A final major drought
after the political collapse of the Maya may be what kept the
civilization from bouncing back.

"Even fairly subtle shifts initially in climate toward drying
appear to have pretty significant ramifications for the social
and political fabric of the Maya world," said study researcher
Douglas Kennett, an environmental anthropologist at Pennsylvania
State University.

The end of the Maya

Kennett and an international group of colleagues — including
climate scientists, archaeologists and experts in Mayan writing —
are not the first to suggest dry spells brought about the
end of the Maya. The Maya lived across southern Mexico and
northern Central America; at their height during the Classic Maya
period from about A.D. 300 to 1000, they gathered in complex
cities of up to 60,000 people. They built stone monuments,
water-storage systems and a complicated astronomical
calendar, which has been widely misinterpreted to predict the
end of the world this December.

Researchers have used geological records of climate from lake
sediments to uncover evidence of drought, but the new study uses
a cave formation to trace a 2,000-year history of rainfall in
more detail than ever before. Researchers removed a stalagmite
from the ground of the cave in a layer that sits close to a
number of Classic Maya settlements. This stalagmite had been
growing slowly but continuously from 40 B.C. to A.D. 2006.
[10
Ways Weather Changed History]

Stalagmites form from calcium carbonate and other minerals left
behind when drips of water move through a cave and evaporate.
Researchers can use uranium-thorium dating (based on those
radioactive elements' rates of decay) to peg down the age of each
layer of a stalagmite. They also can use isotopes, or variants of
chemical elements, to determine how wet it was when each layer
was laid down. (Heavy rainfall carries different isotopes than
light rain does.)

Drought and instability

By analyzing the stalagmite, researchers were able to pin down
rainfall levels twice a year for 2,000 years. They found that
during the early period of Classic Maya civilization, this region
of the world was abnormally wet. Abundant rainfall would have
favored the expansion of the Maya's empire, Kennett told
LiveScience. And sure enough, wet periods in the climate record
coincided with eras of expansion, building and stone monument
construction according to the archaeological record. [Images:
Stunning Maya Murals]

After about A.D. 660, however, things began to change. The
overall climate started to get drier, with more frequent
short-term droughts.

"That's when you also start seeing some indications that there
are stresses in the overall system," Kennett said. War became
more frequent, and some cities began to collapse as people moved
out of population centers. It was the beginning, Kennett said, of
what looks like a two-stage collapse.

The last gasp

An example of the elaborate stone carvings made by
Classical Mayans. This frieze is in Caracol,
Belize.Douglass Kennett, Penn
State

By between 820 and 870, the Maya were struggling to get by on 40
percent less rainfall than before the drying period, the
researchers report in Friday's (Nov. 9) issue of the journal
Science. This period, known as the Terminal Classic, was less
stable than ever before. People began abandoning cities. Building
campaigns ceased. Fewer and fewer stone
monuments were erected.

"It's not all at once," Kennett said. "It's an asynchronous
thing. It's happening over a couple of centuries."

After major political systems failed, smaller agricultural
communities survived into the 1100s and 1200s, Kennett said. It
may have been a second phase of collapse that prevented these
small groups from rebuilding their once-great civilization.
Between about 1020 and 1100, the researchers found, there was an
enormous, crippling drought — the biggest in the entire 2,000
years of the cave record.

"Political systems fail, but then usually something comes back
and sometimes they're even bigger, more integrated. That's a
pattern you see," Kennett said. "That just doesn't really happen
in the Maya region."

The droughts were an example of climate change driven by natural
cycles, Kennett said. (Other research has suggested the Maya
exacerbated the problem by deforestation and other
activities.) The Maya may have been driven by fluctuations in the
intertropical convergence zone, a climate zone that sits along
the equator. When the zone is positioned farther north, you get
wetter conditions in Central America, and when it moves more
southerly, rainfall dries up.

The dry periods and droughts would have set the stage for the
mysteriously abandoned cities the Spanish found when they arrived
in the region in the 1500s, Kennett said.

"That's part of the fascination, I think, with the Maya," he
said. "You have these elaborate cities with stone monuments, with
a
calendar system and a sophisticated hieroglyphic writing
system, and then that just goes away."